1. Field of the Invention
The present invention relates to an image generator which obtains a specular image and a diffuse image from an image acquired by a polarized light field camera by separating two reflection characteristics of a subject, and a control method thereof.
2. Background of the Invention
Every scene we see in our daily lives come into view as the light emitted from a light source hits objects and is then reflected and perceived by our optic nerves. Modeling the color, intensity, and direction of light from a specific type of lighting equipment by a computer by simulating the relationship between light seen through the eyes and a light source is one of the most basic parts of accurate and realistic rendering. To this end, various studies on lighting are being made for realistic 3D rendering in the computer graphics field.
In general, lighting commonly used for rendering a scene in the computer graphics field is categorized into ambient light, diffuse light, and specular light for better efficiency, and the scene is rendered based on the relationship between this light source and the subject surface. The relationship between an object and light in the real world is more complicated because there exist various types of indirect lighting such as light reflected, transmitted, or refracted by other objects, as well as light reflected on the surface. If such indirect lighting is used in 3D modeling, a more realistic representation can be achieved. However, it takes a lot of time to perform rendering, taking into account the effect of light traveling between subjects, and even if rendering is performed over a long time, it is hard to achieve a complex indirect lighting effect such as light scattering within the surface. Accordingly, a variety of methods of applying lighting effects have been developed in computer graphics to give a realistic representation of a scene in a 3D space.
As well as 3D model lighting, research on techniques of splitting a 2D scene into a specular component and a diffuse component has been conducted in the image processing field. Examples of these techniques include a technique of removing the specular component by a PED (partial differential equation) approach, a technique of distributing the specular component and the diffuse component in the chromaticity space of a single image, a technique of defining the specular component and the diffuse component in a 3D space consisting of brightness, saturation, and tone, and a technique of splitting the specular component and the diffuse component by image-based, high-frequency lighting. With these techniques, a diffuse reflection texture map with no specular component can be used in image-based 3D modeling. Also, each component can be individually processed and combined for image editing.
In a paper titled “Fast Separation of Direct and Global Components of a Scene using High Frequency Illumination” (ACM Trans. on Graphics, 2006), the method of obtaining multiple images by a video projector and an ordinary camera and separating a specular image and a diffuse image through a computation process was introduced. In this method, a high-frequency pattern is irradiated on a target scene by a video projector, and multiple images acquired by varying the position of this pattern are computed according to a specific formula, thereby obtaining separate specular and diffuse images.
In a paper titled “Multiview Face Capture using Polarized Spherical Gradient Illumination” (ACM Trans. on Graphics, 2011), the technique of separating specular and diffuse images of a target person and presenting a realistic digital rendering of that person was proposed. Two images are required to separate the specular image and the diffuse image and at least four images are required to obtain 3D reflection information, so a total of 4*2=8 images are required.
To support and increase the functions of 3D modeling, improving the structural part and/or software part of an image generator that separates a specular image and a diffuse image is being considered. Further, there is a growing demand for new image generators capable of fast extracting a specular image and a diffuse image.